The goals of businesses and manufacturers include seeking more ways to increase and generate more profits, promote synergy, expand their venture, and find ways to increase the efficiency and productivity of their business. Lean manufacturing methods are needed to achieve these objectives; particularly, by putting an emphasis on workflow. When it comes to one of the most effective yet simple lean methods for focusing on customer value and improving business efficiency, one of the best solutions is One Piece Flow.
What is One Piece Flow?
This is a fundamental element in lean manufacturing regarding what can be achieved after much waste has been eliminated from the shop floor. One piece flow, also known as single piece flow, is an ideal state of efficient operations where products are work on one at a time instead of using batch sizes and lot production. This is not possible in every operation, particular ones with high changeover times and low processing times which is determined using takt time data.
When an organization tries to attain one-piece flow, numerous other activities are set in motion to eliminate all forms of muda (waste). Many companies have failed in their attempts to reach a level of one piece flow since it is the epitome of flow and has now reached a fad status among many industries. Fully achieving one piece flow is extremely hard for most companies because it requires very specific conditions and a highly refined process.
In manufacturing, one piece flow is where a single piece is placed between workstations. There is usually minor variance in each workers cycle time that does not cause any waiting time. In an optimal situation, there should be an exceptionally high cycle balance between operations. The higher the number of pieces in each operation, the greater the variation in cycle times from operation to operation. This is where the risk of overproduction occurs and it requires knowing when to decrease the buffer between operations and increase the losses due to work times that are imbalanced.
Key Criteria for Achieving Flow
Here are the foundational elements that are critical for achieving one piece flow:
- Operation cycle times must be equal to the takt time. Companies that have overproduction and long waiting times are often because of uneven work times.
- Reliance on Equipment and Process. It is imperative that there is a constant focus on the equipment and processes to include changeover, downtime, ease-of-use, and simplicity-of-use.
- Ensure consistent capability which is a foundational element that is necessary for achieving one piece flow. The level of capability should be on a daily basis, and during each day of operation, it is capable of fulfilling the requirements of the customer.
- Consistent capability requires consistent availability and application of resources to include people, equipment, and materials. One of the primary reasons that flow is often unsuccessful is because of the inconsistent availability of these resources. It is up to your team to put measures in place to ensure the availability of resources. This should not include just adding resources alone because this translates into added cost.
One piece flow concentrates on finishing the production of one piece from the beginning until it is finished with as little Work in Process (WIP) inventory as possible between operations. In a one-piece flow system, one item is completed for each item started. Whenever possible, operations are placed in a “U” shape, and the flow is from right to left (counterclockwise). A minimum of one piece of work in process at each step will facilitate the flow of most processes.
One Piece Flow When Making Peanut Butter and Jelly Sandwiches
An easy example to explain one piece flow is to look at the two ways to build a peanut butter and jelly sandwich. If you use the traditional batch method, you would take three pieces of bread and spread peanut butter on them. Next, you will take three more pieces of bread and place jelly on them. Then, take the opposite sides and marry them together to make three sandwiches.
The one piece flow approach involves taking one piece of bread and putting peanut butter on it and then putting jelly on another piece. These two pieces are married together, and steps are repeated two more times until you have three peanut butter and jelly sandwiches. The one piece approach is better because the cycle time is shorter and sandwiches are completed in each motion. There is no waiting involved.
Put Them to the Test
Everyone thinks the batch flow is faster than one piece flow and this is not always the case. For example, the next time you have dirty dishes, get a partner and time yourself. One person will wash the dishes using the batch method, and the other will use the one piece flow method. The batch method will require you to wash and rinse the dishes and then set each one aside and then continued this step until all dishes are clean. Next, you will dry and put away one dish at a time.
Using the one piece flow method, your partner will wash, rinse, dry, and put away a single dish and then move on to the next one. When you time both methods, you may be surprised to find out that the one piece flow method is usually faster.
How a One Piece Flow is More Efficient
According to Toyota which founded this principal, each operation only builds what the next operation needs in a true one piece flow. If there is a backup in the next operation for any reason, then preceding operations will stop. In a manufacturing environment, a stoppage is something all manufacturers want to avoid which leads to another problem – overproduction.
Overproduction can include producing sooner, more, or in greater quantity than the next operation requires. Companies like Toyota consider overproduction to be one of the worst types of waste because it leads to the creation of many others to include problems with inventory, handling, movement, hidden defects, etc.
For one piece flow to be more efficient, organizations must understand how less can be more. This can translate into improved efficiency by producing fewer parts in some individual steps in the process and getting more value-added activity done from the overall process.
How It Benefits Businesses
Here are a few benefits for organizations when one piece flow is successfully implemented:
Builds in Quality.
One major benefit that gets pointed out time and time again with one piece flow is that defects are detected immediately. Usually, the next workstation will force immediate corrective action. This is in contrast to the batch method which may include an entire batch that has the same defect.
One piece flow limits the need for containers of material or having to lift heavy pallets. Since overexertion is one of the main sources of injury in the workplace, one piece flow makes the workplace safer.
There are several common ways that are associated with batching and queue production to include waiting, motion, transportation, among many others. All of these negative factors are greatly reduced with one piece flow which leads to an increase in productivity.
This system is known to be faster than batch and queue and allows you to wait longer to schedule an order and still deliver on time it also helps to respond to last-minute changes from the customer. Customers love to change their mind all the time, and flow provides better response times.
Work in Process (WIP) is significantly reduced which means you do not have to manage, move, and store huge piles of inventory.
Equipment can be designed smaller and at a lower cost since it is no longer needed to produce huge batches of material at breakneck speed.
Simplifies material replenishment.
When paced at takt time, one piece flow allows for material delivery to be completed by set quantity deliveries or timed milk runs.
Employees want to do good work and see progress by getting involved. One flow is a method to bring everyone together.
Frees Up Floor Space.
The amount of WIP on the floor is reduced, so there is more floor space freed up. Also, workstations must be connected and not be in their isolated area.
Kaizen Will Take Root.
One piece flow does not allow you to hide behind the buffers of inventory. Therefore, quality must improve, changeovers must be shortened, and machine reliability must increase, among other factors. However, this process allows kaizen to take root.
How to Implement a One Piece Flow
For one piece flow to work effectively, all of the following conditions must be met:
- Processes must be able to produce a good product consistently. One piece flow is not possible where there are quality issues.
- Process times can be repeated. One piece flow is impossible if there is variation.
- Equipment must have a very high uptime percentage (near 100%). Your equipment must always be able to run. One piece flow is not possible if any equipment within a manufacturing cell is plagued with downtime.
- Processes must be scaled to the rate of customer demand or takt time. If takt time is every 12 minutes, processes should be able scaled to run at one unit every 12 minutes.
Implementing a One Piece Flow Cell
When implementing this step, the first thing to do is to decide which products or product families will go into the cells once the type of cells has been determined. The next step is to calculate the takt time for the set of products that will be assigned to each cell. Takt time can be measured using the following formula:
Takt time (equals) Available work time per shift (divided by) Customer demand per shift
The next step is to determine the work elements and time that is needed for making each piece. List each step and its associated time in as much detail as possible. Next, time each step individually several times and use the lowest repeatable time after you have repeated this process a few times. It is important to make sure the equipment that will be used can meet takt time, and this will be based on a few considerations to include downtime, changeover times, and load and unload times.
Next, you must create a lean layout using 5S. Space is also a consideration, and U-shaped cells are usually the best setup. Finally, balance the cell and create standardized work procedures for each operator within the cell.
You can determine how many operators are needed to meet takt time and then divide the work among operators by using this formula:
Number of operators (equals) total work content (divided by) takt time
After you have successfully implemented one piece flow, you must sustain it through regular auditing of standardized work.
A Key Concept
Within lean manufacturing, one piece flow is a key concept since the value stream can be transformed into a one piece flow operation. Lean manufacturing puts an emphasis on workflow, focusing on customer value, and improving business. One piece flow helps organizations accomplish these goals by reducing work expenses and eliminating waste.